diff --git a/src/kits/interface/RegionSupport.cpp b/src/kits/interface/RegionSupport.cpp
index 72aca4d92d..4cc09f1c93 100644
--- a/src/kits/interface/RegionSupport.cpp
+++ b/src/kits/interface/RegionSupport.cpp
@@ -85,7 +85,7 @@ using std::nothrow;
 #ifdef DEBUG
 #include <stdio.h>
 #define assert(expr) {if (!(expr)) fprintf(stderr,\
-"Assertion failed file %s, line %d: expr\n", __FILE__, __LINE__); }
+"Assertion failed file %s, line %d: " #expr "\n", __FILE__, __LINE__); }
 #else
 #define assert(expr)
 #endif